A variety of medical conditions are treatable by the implantation of tubular devices into natural body lumens. For example, it is commonplace to implant metallic stents into the coronary arteries of patients with heart disease following balloon angioplasty to minimize the risk that the arteries will undergo restenosis. Recently, commercial stents have included drug-eluting polymer coatings that are designed to further decrease the risk of restenosis. Other examples of conventional tubular medical implants include woven grafts and stent-grafts that are used to span vascular aneurysms, polymeric tubes and catheters that are used to bypass strictures in the ureter and urethra, and stents that are used in the peripheral vasculature, prostate, sinus and esophagus. It should be recognized that the size of the devices of the present invention will depend upon their clinical application. For example, stents for the esophagus and other large bodily lumens may be as large as 30 mm or 40 mm in diameter or larger.
Despite the evolution of metallic stents, they continue to have limitations such as the possibility of causing thrombosis, restenosis and vascular remodeling. While the use of biodegradable and biostable polymeric materials for stents and other implantable devices has been proposed to eliminate the possible long-term effects of permanent implants, the use of such materials has been hindered by relatively poor expandability and mechanical properties. For example, the expansion characteristics and radial strength of prototype stents made from biodegradable and biostable polymeric materials has been significantly lower than that of metallic stents. This is particularly the case where such stents are low profile and make use of small diameter fibers or thin walled struts that comprise the stent body. Furthermore, the degradation rate and the manner in which such devices degrade in the body have been difficult to control. Finally, where such devices are used as a drug delivery vehicle, the drug elution rate has been difficult to reproducibly characterize.
There is therefore a need for low-profile, self-expanding implantable tubular devices that have sufficient expansion characteristics, strength and other mechanical and drug release properties that are necessary to effectively treat the medical conditions for which they are used. There is also generally a need to provide such devices that include the lowest possible dose of drug that is able to provide clinically effective results.